This invention relates to a method of controlling the reaction exotherm in the polymerization of acetylene terminated compounds. More particularly, this invention relates to a method for preventing charring and decomposition during polymerization by heating a mixture of an acetylene terminated monomer and its corresponding prepolymer.
Conjugated aromatic acetylene terminated Schiff's bases can be thermally polymerized into thermosets, as described in U.S. Pat. No. 4,178,430 to Bilow. These polymers are of particular interest because the extended conjugated pi electron system presents the possibility of electrically conducting polymers. The polymers also show the capacity to withstand harsh environmental conditions.
The acetylene end groups polymerize thermally. Heat treatment must be carefully controlled in order to prevent charring, foaming and decomposition. This control is difficult to achieve due to self-heating and poor heat dissipation in the bulk sample. Heating slowly may not guarantee good results, as the heat is internally generated. One previous attempt to solve this problem is described in Walton, Journal of Applied Polymer Science, Vol. 37, pp. 1921-1929 (1989), who partially b-staged the resins,, thereby lowering the recrystallization temperature and allowing curing at lower temperatures. Although this technique slightly improved the window of processability for these polymers, it did not successfully control the reaction exotherm. Until now, good heat dissipation has required limiting the size or thickness of the sample. A method of controlling the reaction exotherm f or these polymers is currently greatly needed.
It is therefore an objective of the present invention to provide a method for controlling the reaction exotherm of acetylene terminated monomers.